A conventional technology for applying an electric field to a liquid crystal composition layer is proposed, for instance, in Japanese Laid-Open Patent Publication No. 7-36058 and No. 7-159786 in which an electric field is applied to a pair of comb like electrodes formed on a substrate of an active matrix type liquid crystal display device. Heretofore, a display system in which a direction of a primary electric field applied to a liquid crystal composition layer is substantially parallel with a surface of the substrate is referred to as a transverse electric field system.
FIG. 1 shows such a conventional example of a transverse electric field system. In this example, comb like pixel electrodes 5 and 6 are straight and positioned in parallel with one another.
In the above-described transverse electric field system having a conventional pixel electrode structure of FIG. 1, it is known that visual field angle characteristics will change drastically with the change of a pretilt angle as shown in FIG. 10. Thus, in order to achieve good visual angle characteristics in the transverse electric field system, a combination of an alignment film of a very small pretilt angle and liquid crystal is required. According to the experiment, it is desirable that a pretilt angle is less than one (1) degree as shown in FIG. 10.
However, in a vertical electric field system incorporated in liquid crystal displays most widely used today have a pretilt angle of 3–8 degrees between an alignment film and liquid crystal. The vertical electric field system is a display system wherein a direction of a primary electric field is almost vertical to the surface of a substrate. When an alignment film and liquid crystal with one (1) degree of pretilt are used in a liquid crystal display of the vertical electric field system, a reverse tilt domain will be created by the electric field of video signal lines and pixel electrodes, resulting in a significant deterioration in the display quality.
Because of the foregoing reasons, a set of alignment film and liquid crystal to be used in a liquid crystal display based on the transverse electric field system is different from a set of alignment film and liquid crystal to be used in a liquid crystal display system based on the vertical electric field system. When producing liquid crystal display devices of different display systems by the same production facility, alignment films and liquid crystal must be constantly changed, which decreases a production efficiency.